1) I can't get R to recognize the functions f and f. if I try using readline() to prompt for user input. I get the error "Error in Newton() : could not find function "f."" However, if I comment out the readlines (as above), define f and f. beforehand, and then everything works fine.

2) I've been trying to make R calculate the derivative of a function. The problem is that the class object with which R can take symbolic derivatives is expression(), but I want to take the derivative of a function() and have it give me a function(). In short, I'm having trouble with type conversion between expression() and function(). I have an ugly but effective solution for going from function() to expression(). Given a function f, D(body(f)[[2]],"x") will give the derivative of f. However, this output is an expression(), and I haven't been able to turn it back into a function(). Do I need to use eval() or something? I've tried subsetting, but to no avail. For instance: